1. Field of the Invention
The invention relates to a drive device for a vehicle part that is displaceable between end positions, in particular for a cover of an openable vehicle roof with an electric motor that is connected by a reduction gear to a pinion gear on an output shaft, the pinion gear having a driving connection to the adjustment part by power transmission means, and with at least one switch controlling the electric motor to stop the electric motor in at least one predetermined position of the adjustable part. Furthermore, to actuate the switch, a switch wheel of an eccentric wheel gear is provided that has a driving connection, by an input shaft, to the reduction gear.
2. Description of Related Art
A generic drive device is known from U.S. Pat. No. 5,181,891 in which a switch element for the driving electric motor is actuated by an eccentric wheel gear, offering a relatively simple design and high actuated by an eccentric wheel gear, offering a relatively simple design and high switching precision, especially for the end positions of the part to be adjusted. The drawback of the arrangement disclosed in this patent is that, with a possible failure of the electric motor, no emergency actuation device is provided for manually closing the displaceable part.
An emergency actuation device with which an electric drive motor can be uncoupled for manual emergency actuation by axially shifting an input shaft is known from published European Patent Application 0 410 487 A2. However, the drive shown there has no gear parts placed coaxial to the input shaft to trigger the switching operations.
In another drive device used by the assignee of the applicant, it is true that such an eccentric wheel gear, coaxial to the input shaft, is present, but, with an axial shifting of the input shaft during an emergency actuation operation, the eccentric wheel gear, like the worm wheel coupled with the electric motor, is brought out of mesh. This results in the drawback that, after an emergency actuation, the gearwheels provided for normal drive and the gearwheels provided for the switching actuations have lost their original reference positions that were matched exactly to each other. Thus, after an emergency actuation that is attributable to problems in the voltage supply of the vehicle and not a defective drive, nonetheless, a costly stay in the repair shop for a readjustment of the overall drive is necessary.
In the case of U.S. Pat. No. 4,841,812, a drive device for the cover of sliding and lifting roofs uses a planetary gear assembly which automatically produces a different gearing ratio when operated in one direction than in another direction by a drive motor. The drive shaft has an axial extension which has a hexagonal socket within which an appropriate tool can be engaged for operation of the drive in the event of a malfunction of the electric motor or an inadequate current supply. However, no means for disconnecting the drive from the motor is described so that considerable effort would required to overcome the resistance of an inoperative motor.